There are a number of patent specifications which describe how the geographical position of a mobile station could be established with the aid of a mobile communications system. In those patent specifications that describe how the position of a mobile station could be determined with relatively good precision, the actual measuring procedure itself is the essential problem. The measuring procedure determines the distance between a mobile station and one or more radio base stations. Normally, the distance between the mobile station and at least three base stations is measured. When the geographical positions of the base stations are known, the position of the mobile station can then be determined in accordance with the triangulation method. These patent specifications can be divided into two groups of which those specifications in one group deal with uplink measuring processes, i.e. in the base station, and the other group deals with downlink measuring processes, i.e. in the mobile station.
SE 9603561-3 is a patent specification that belongs to the first group. This patent specification describes how the distances between the mobile station and a number of base stations are determined by measuring the wave propagation delay. This delay is measured in a second of the base stations, when the mobile station during an established connection with a first base station makes access to this second base station, such as in the case of a typical handover. The transmission time point of the transmitted access signal is not adapted to compensate for the wave propagation delay and therefore arrives late at the second base station in relation to the correct time position. This delay, i.e. propagation delay, is measured by the radio base station, whereafter the transfer is interrupted and the mobile station renews the connection with the first base station. The patent specification does not describe how the positioning procedure shall be initiated or which node coordinates and controls the measuring process. The patent specification mentions that positional data is transferred to a positioning node, where the position of the mobile station is established.
Swedish Patent Specification SE 96005772 is an example of those patent specifications that belong to the second group, i.e. the group in which the mobile station performs the measuring process. Subsequent to having measured the time delay of signals from several base stations, the mobile station sends the measured values together with the identities of the base stations to a positioning node, where the position of the mobile station is calculated.
Both of the aforementioned patent specifications teach a solution to the problem of performing a measuring process for determining the position of a mobile station. However, more problems than the problem of the actual measuring procedure must be solved in order to be able to offer a positioning service in a mobile communications system to a large group of users. One such problem which none of the aforesaid patent specifications provides a solution is how the positioning procedure could be initiated upon request by a user. Another problem is how the positional data shall be transferred to the positioning node.